U.S. patent application number 11/143333 was filed with the patent office on 2007-01-11 for flame retardant emi shields.
Invention is credited to Larry D. JR. Creasy.
Application Number | 20070011693 11/143333 |
Document ID | / |
Family ID | 37215160 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070011693 |
Kind Code |
A1 |
Creasy; Larry D. JR. |
January 11, 2007 |
Flame retardant EMI shields
Abstract
An electromagnetic interference shield generally includes a
resilient core member and an electrically conductive layer. An
adhesive bonds the electrically conductive layer to the resilient
core member. The adhesive can include halogen-free flame retardant.
The electrically conductive layer can be provided with halogen-free
flame retardant and/or a corrosion inhibitor.
Inventors: |
Creasy; Larry D. JR.; (St.
Clair, MO) |
Correspondence
Address: |
Anthony G. Fussner;Suite 400
7700 Bonhomme
St. Louis
MO
63105
US
|
Family ID: |
37215160 |
Appl. No.: |
11/143333 |
Filed: |
June 2, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60651252 |
Feb 9, 2005 |
|
|
|
Current U.S.
Class: |
720/650 ;
428/317.1 |
Current CPC
Class: |
C08K 5/49 20130101; H05K
9/0088 20130101; Y10T 428/249953 20150401; Y10T 428/249982
20150401; Y10T 428/28 20150115 |
Class at
Publication: |
720/650 ;
428/317.1 |
International
Class: |
G11B 33/14 20060101
G11B033/14; B32B 7/12 20060101 B32B007/12 |
Claims
1. An electromagnetic interference (EMI) shield comprising at least
one resilient core member, at least one electrically conductive
layer provided with at least one halogen-free flame retardant, and
at least one adhesive bonding the electrically conductive layer to
the resilient core member, the adhesive including an effective
amount of at least one halogen-free flame retardant less than a
predetermined percentage by dry weight below which the adhesive
provides at least a predetermined bond strength, the halogen-free
flame retardant provided to the electrically conductive layer and
the effective amount of halogen-free flame retardant within the
adhesive being effective at providing the shield with a
predetermined flame rating.
2. The shield of claim 1, wherein the predetermined bond strength
is at least about ten ounces per inch width, and wherein the
predetermined flame rating is a flame rating of V0 under
Underwriter's Laboratories (UL) Standard No. 94.
3. The shield of claim 1, wherein the halogen-free flame retardant
provided to the electrically conductive layer and the effective
amount of halogen-free flame retardant within the adhesive are
effective at providing the shield with a flame rating of V0 under
Underwriter's Laboratories (UL) Standard No. 94.
4. The shield of claim 3, wherein the adhesive provides a bond
strength of at least about ten ounces per inch width.
5. The shield of claim 3, wherein the effective amount of
halogen-free flame retardant within the adhesive is about fifty
percent by dry weight.
6. The shield of claim 3, wherein the effective amount of
halogen-free flame retardant within the adhesive is about
sixty-three percent by dry weight.
7. The shield of claim 3, wherein the effective amount of
halogen-free flame retardant within the adhesive is about
fifty-five percent by dry weight.
8. The shield of claim 3, wherein the effective amount of
halogen-free flame retardant within the adhesive is within a range
of about fifty percent to sixty-three percent by dry weight.
9. The shield of claim 8, wherein the electrically conductive layer
comprises at least one fabric material, the resilient core member
comprises at least one foam material, the adhesive includes at
least one halogen-free phosphorous-based flame retardant, and the
halogen-free flame retardant provided to the electrically
conductive layer comprises urethane.
10. The shield of claim 8, wherein the halogen-free flame retardant
provided to the electrically conductive layer comprises urethane,
and wherein the weight pick-up of the halogen-free flame retardant
including the urethane is between about 0.16 ounces per square yard
and about 0.33 ounces per square yard.
11. The shield of claim 8, wherein the halogen-free flame retardant
provided to the electrically conductive layer comprises about
fifty-four percent by dry weight of a phosphorous-based flame
retardant and about forty-six percent by dry weight of
urethane.
12. The shield of claim 8, wherein the halogen-free flame retardant
provided to the electrically conductive layer comprises urethane,
and wherein the weight pick-up of the halogen-free flame retardant
including the urethane is about 0.27 ounces per square yard.
13. The shield of claim 8, wherein the halogen-free flame retardant
provided to the electrically conductive layer comprises urethane
and a corrosion inhibitor, and wherein the weight pick-up of the
halogen-free flame retardant including the urethane and the
corrosion inhibitor is between about 0.05 ounces per square yard
and about 0.35 ounces per yard.
14. The shield of claim 8, wherein the halogen-free flame retardant
provided to the electrically conductive layer comprises urethane
and a corrosion inhibitor, and wherein the weight pick-up of the
halogen-free flame retardant including the urethane and the
corrosion inhibitor is about 0.15 ounces per square yard.
15. The shield of claim 8, wherein the halogen-free flame retardant
provided to the electrically conductive layer comprises about four
percent by dry weight of a corrosion inhibitor and about ninety-six
percent by dry weight of urethane.
16. The shield of claim 8, wherein the halogen-free flame retardant
is provided to the electrically conductive layer in an amount such
that the electrically conductive layer maintains a surface
resistivity of less than about 0.1 ohms/sq.
17. The shield of claim 1, wherein the halogen-free flame retardant
provided to the electrically conductive layer is a corrosion
inhibitor.
18. A method of making an electromagnetic interference (EMI) shield
having at least one resilient core member and at least one
electrically conductive layer, the method comprising applying at
least one halogen-free flame retardant to the electrically
conductive layer, and bonding the electrically conductive layer to
the resilient core member with at least one adhesive including an
effective amount of at least one halogen-free flame retardant less
than a predetermined percentage by dry weight below which the
adhesive provides at least a predetermined bond strength, the
halogen-free flame retardant provided to the electrically
conductive layer and the effective amount of halogen-free flame
retardant within the adhesive being effective at providing the
shield with a predetermined flame rating.
19. The method of claim 18, wherein the predetermined flame rating
is a flame rating of V0 under Underwriter's Laboratories (UL)
Standard No. 94.
20. The method of claim 18, wherein bonding the electrically
conductive layer resilient core member with at least one adhesive
provides a bond strength of at least about ten ounces per inch
width.
21. The method of claim 18, wherein applying at least one
halogen-free flame retardant to the electrically conductive layer
includes applying at least one corrosion inhibitor to the
electrically conductive layer.
22. The method of claim 18, further comprising selecting the
adhesive such that the predetermined bond strength is at least
about ten ounces per inch width, and the predetermined flame rating
is a flame rating of V0 under Underwriter's Laboratories (UL)
Standard No. 94.
23. An electromagnetic interference (EMI) shield comprising at
least one resilient core member, at least one electrically
conductive, and at least one adhesive bonding the electrically
conductive layer to the resilient core member, the adhesive
including an amount of halogen-free flame retardant within a range
of about fifty percent to about sixty-three percent by dry weight
such that the shield has a flame rating of V0 under Underwriter's
Laboratories (UL) Standard No. 94.
24. The shield of claim 23, wherein the adhesive includes about
fifty percent by dry weight of halogen-free flame retardant.
25. The shield of claim 23, wherein the adhesive includes an amount
of halogen-free flame retardant less than a predetermined
percentage by dry weight below which the adhesive provides at least
a predetermined bond strength.
26. The shield of claim 23, wherein the predetermined bond strength
is at least about ten ounces per inch width.
27. The shield of claim 23, further comprising halogen-free flame
retardant provided to the electrically conductive layer.
28. The shield of claim 27, wherein the halogen-free flame
retardant provided to the electrically conductive layer is a
corrosion inhibitor.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application 60/651,252, filed Feb. 9, 2005, the entire disclosure
of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention generally relates to electromagnetic
interference (EMI) shielding, and more particularly (but not
exclusively) to flame retardant fabric-over-foam EMI shields formed
from environmentally friendly materials, such as halogen-free flame
retardants.
BACKGROUND OF THE INVENTION
[0003] The operation of electronic devices generates
electromagnetic radiation within the electronic circuitry of the
equipment. Such radiation results in electromagnetic interference
(EMI), which can interfere with the operation of other electronic
devices within a certain proximity. A common solution to ameliorate
the effects of EMI has been the development of shields capable of
absorbing and/or reflecting EMI energy. These shields are typically
employed to localize EMI within its source, and to insulate other
devices proximal to the EMI source.
SUMMARY OF THE INVENTION
[0004] According to one aspect of the present invention, an EMI
shield generally includes a resilient core member and an
electrically conductive layer. An adhesive bonds the electrically
conductive layer to the resilient core member. The adhesive
includes halogen-free flame retardant. In various embodiments, the
electrically conductive layer can be provided with halogen-free
flame retardant and/or a corrosion inhibitor.
[0005] In another aspect, the invention provides methods of making
EMI shields. In one exemplary implementation, the method generally
includes applying halogen-free flame retardant and/or a corrosion
inhibitor to an electrically conductive layer, and bonding the
electrically conductive layer to a resilient core member with an
adhesive including halogen-free flame retardant.
[0006] Further aspects of the present invention will become
apparent from the detailed description provided hereinafter. It
should be understood that the detailed description and specific
examples, while indicating various embodiments and methods of the
invention, are for illustration purposes only and are not intended
to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention will become more fully understood from the
detailed description and the accompanying drawings, wherein:
[0008] FIG. 1 is a perspective view of an EMI shield according to
one exemplary embodiment of the present invention;
[0009] FIG. 2 is an exemplary line graph of load versus time
showing bond strength of an adhesive that includes halogen-free
flame retardant according to one exemplary embodiment of the
present invention;
[0010] FIG. 3 is an exemplary line graph of load versus time
showing bond strength of an adhesive that includes halogen-free
flame retardant according to one exemplary embodiment of the
present invention;
[0011] FIG. 4 is a table of exemplary fabrics that can be provided
with halogen-free flame retardant according to various exemplary
embodiments of the present invention;
[0012] FIG. 5 is a table summarizing data collected during crush
and fold testing of a nylon ripstop (NRS) fabric coated with
urethane, and a NRS fabric coated with halogen-free flame retardant
urethane according to one exemplary embodiment of the present
invention;
[0013] FIG. 6 is an exemplary line graph of created with data from
the table shown in FIG. 5 and illustrating surface resistivity
versus number of cycles during the crush and fold testing;
[0014] FIG. 7 is an exemplary line graph of surface resistivity
versus number of cycles during inflated diaphragm abrasion testing
of a NRS fabric coated with urethane, and a NRS fabric coated with
halogen-free flame retardant urethane according to one exemplary
embodiment of the present invention;
[0015] FIG. 8 is an exemplary line graph of shielding effectiveness
versus frequency for a NRS fabric coated with urethane, and a NRS
fabric coated with halogen-free flame retardant urethane according
to one exemplary embodiment of the present invention;
[0016] FIG. 9 is an exemplary line graph of shielding effectiveness
versus frequency for the NRS fabrics shown in FIG. 8 after one week
of exposure at sixty degrees Celsius and ninety percent relative
humidity;
[0017] FIG. 10 is another exemplary line graph of shielding
effectiveness versus frequency for the NRS fabrics shown in FIGS. 8
and 9 after two weeks of exposure at sixty degrees Celsius and
ninety percent relative humidity;
[0018] FIG. 11 is another exemplary line graph of shielding
effectiveness versus frequency for the NRS fabric coated with
halogen-free flame retardant urethane shown in FIGS. 8-10 after
eight weeks of exposure at sixty degrees Celsius and ninety percent
relative humidity; and
[0019] FIG. 12 is an exemplary line graph of load versus time
showing bond strength of an adhesive that includes halogen-free
flame retardant according to one exemplary embodiment of the
present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0020] The following description of the exemplary embodiments is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0021] According to various aspects, the invention provides
electromagnetic interference (EMI) shields, such as EMI gaskets. In
one embodiment, an EMI shield generally includes a resilient core
member and an electrically conductive layer. The electrically
conductive layer is provided with (e.g., coated, impregnated,
combinations thereof, etc.) halogen-free flame retardant. An
adhesive bonds the electrically conductive layer to the core
member. The adhesive is loaded with an effective amount of
halogen-free flame retardant, which in combination with the
halogen-free flame retardant provided to the electrically
conductive layer, enables the shield to achieve a predetermined
flame retardant rating (e.g., a UL 94 vertical flame rating of V0,
etc.). The effective amount of halogen-free flame retardant in the
adhesive, however, is less than a predetermined percentage below
which the loaded adhesive provides at least a predetermined bond
strength (e.g., at least about ten ounces per inch width as
determined, for example, by a one hundred eighty degree peel test
at twelve inches per minute, etc.). Accordingly, this particular
embodiment of the EMI shield is halogen-free and environmentally
friendly.
[0022] In another embodiment, an EMI shield generally includes a
resilient core member and an electrically conductive layer. The
electrically conductive layer is bonded to the core member with an
adhesive. In this particular embodiment, the adhesive is loaded
with an effective amount of halogen-free flame retardant such that
the shield can achieve a predetermined flame retardant rating
(e.g., a UL 94 vertical flame rating of V0, etc.) without flame
retardant being provided to the electrically conductive layer. The
effective amount of halogen-free flame retardant in the adhesive,
however, is less than a predetermined percentage below which the
loaded adhesive provides at least a predetermined bond strength
(e.g., at least about ten ounces per inch width as determined, for
example, by a one hundred eighty degree peel test at twelve inches
per minute, etc.). Accordingly, this particular embodiment of the
EMI shield is halogen-free and environmentally friendly.
[0023] In a further embodiment, an EMI shield generally includes a
resilient core member and an electrically conductive layer. An
adhesive, which includes halogen-free flame retardant, bonds the
electrically conductive layer to the core member. In this
particular embodiment, the electrically conductive layer is
provided with (e.g., coated, impregnated, combinations thereof,
etc.) a halogen-free corrosion inhibitor (e.g., benzotriazole, or
other suitable corrosion inhibitor, for example, from the azole
family and/or pyrole family, etc.). The corrosion inhibitor can
also function as a flame retardant, which in combination with the
flame retardant properties of the adhesive enables the shield to
achieve a predetermined flame retardant rating (e.g., a UL 94
vertical flame rating of V0, etc.). The effective amount of
halogen-free flame retardant in the adhesive, however, is less than
a predetermined percentage below which the loaded adhesive provides
at least a predetermined bond strength (e.g., at least about ten
ounces per inch width as determined, for example, by a one hundred
eighty degree peel test at twelve inches per minute, etc.).
Accordingly, this particular embodiment of the EMI shield is
halogen-free and environmentally friendly.
[0024] Other aspects of the invention methods of making and using
EMI shields. Further aspects of the invention include adhesives
loaded with halogen-free flame retardant. Additional aspects of the
invention include electrically conductive materials (e.g., nylon
ripstop (NRS) fabrics, mesh fabrics, taffeta fabrics, woven
fabrics, non-woven fabrics, knitted fabrics, etc.) that are
provided with (e.g., coated, impregnated, combinations thereof,
etc.) halogen-free flame retardants and/or corrosion inhibitors.
Further aspects include EMI shields in which the electrically
conductive layer is not provided with flame retardant or a
corrosion inhibitor.
[0025] FIG. 1 illustrates an exemplary EMI shield 20 in accordance
with principles of the present invention. As shown, the shield 20
includes a resilient core member 22, an electrically conductive
layer 26 generally surrounding the resilient core member 22, and an
adhesive 24 bonding the electrically conductive layer 26 to the
resilient core member 22. The electrically conductive layer 26 can
be provided (e.g., coated, impregnated, combinations thereof, etc.)
with halogen-free flame retardant and/or a halogen-free corrosion
inhibitor (which may also function as and thus be referred to
herein as a flame retardant). In the illustrated embodiment, the
electrically conductive layer 26 is provided a coating 28 that
includes halogen-free flame retardant and urethane. In addition to,
or as an alternative, to the flame retardant, the coating 28 can
include a corrosion inhibitor such as benzotriazole or other
suitable corrosion inhibitors, for example, selected from the azole
family and/or pyrole family. In various embodiments, the corrosion
inhibitor may have flame retardant properties, in which case, the
coating need not include any other flame retardants besides the
corrosion inhibitor.
[0026] A wide range of materials can be used for the resilient core
member 22. In one embodiment, the resilient core member 22 is made
of urethane foam having a polyester film scrim attached thereto.
Alternatively, other materials can be used for the resilient core
member, such as other resiliently compressible materials that are
suitable for compression within an opening. Other materials and
types can also be used for the scrim including fabrics. Yet other
embodiments do not have a scrim attached to the resilient core
member.
[0027] A wide range of materials can be used for the electrically
conductive portion 26. Exemplary materials include conductive
fillers within a layer, a metal layer, and/or a conductive
non-metal layer. In some embodiments, the electrically conductive
portion 26 comprises a metallized or plated fabric in which the
metal is copper, nickel, silver, palladium aluminum, tin, alloys,
and/or combinations thereof. For example, one particular embodiment
includes a nickel copper nylon ripstop (NRS) fabric. In other
embodiments, the electrically conductive portion 26 may comprise a
layer of material that is impregnated with a metal material to
thereby render the layer sufficiently electrically conductive for
EMI shielding applications. The particular material(s) used for the
electrically conductive portion 26 may vary, for example, depending
on the desired electrical properties (e.g., surface resistivity,
electrical conductivity, etc.), which, in turn, can depend, for
example, on the particular application in which the EMI shield will
be used.
[0028] In various embodiments, the adhesive layer 24 is an
environmentally safe adhesive suitable for providing good bond
strength between the electrically conductive portion 26 and the
resilient core member 22. The adhesive layer 24 can include a wide
range of suitable adhesives. In one embodiment, the adhesive layer
24 includes a solvent based polyester adhesive that is loaded with
an effective amount of flame retardant to enable the EMI shield to
achieve a predetermined flame rating while at the same time having
good bond strength and retaining properties suitable (e.g.,
shielding effectiveness, bulk resistivity, etc.) for EMI shielding
applications.
[0029] Flame ratings can be determined using the Underwriters
Laboratories Standard No. 94, "Tests for Flammability of Plastic
Materials for Parts in Devices and Appliances" (5.sup.th Edition,
Oct. 29, 1996) or using an ASTM (American Society for Testing and
Materials) flammability test. In one embodiment, the adhesive layer
24 includes an effective amount of flame retardant such that the
EMI shield 20 has a UL 94 vertical flame rating of V0. In other
embodiments, the adhesive layer may include less flame retardant
(or lesser effective flame retardants) such that the EMI shield can
only achieve a lower UL94 flame rating such as V1, V2, HB, or HF-1.
The desired UL94 flame rating can depend, for example, on the
particular application or installation for the EMI shield.
[0030] While the adhesive can include at least an effective amount
of halogen-free flame retardant to achieve a predetermined flame
rating, the adhesive can also include more than that effective
amount. In various embodiments, the adhesive does not include more
than a predetermined percentage by dry weight of the halogen-free
flame retardant, below which percentage the adhesive provides at
least a predetermined bond strength. As recognized by the inventor
hereof, there is a delicate balance that should be maintained with
the halogen-free flame retardant and the adhesive for some
embodiments of the invention. If the adhesive contains too much
halogen-free flame retardant, the bond strength can be compromised.
But if the adhesive does not include enough halogen-free flame
retardant, then the EMI shield may not be able to meet the desired
UL94 flame rating (e.g., V0, V1, V2, HB, HF-1, etc.). Accordingly,
in various embodiment, the adhesive includes at least an effective
amount of halogen-free flame retardant for providing the shield
with a predetermined UL flame rating, but less than a predetermined
percentage below which the adhesive provides at least a
predetermined bond strength.
[0031] In various embodiments, the halogen-free flame retardant is
a phosphorous-based flame retardant. In one embodiment, the
adhesive includes an amount of halogen-free flame retardant of at
least about thirty percent (.+-.five percent) but not more than
about seventy percent by dry weight. In another embodiment, the
adhesive includes an amount of halogen-free flame retardant of at
least about fifty percent but not more than about sixty-three
percent by dry weight. In yet another embodiment, the adhesive
includes an amount of halogen-free flame retardant of about
sixty-three percent by dry weight. In still another embodiment, the
adhesive includes an amount of halogen-free flame retardant of
about fifty-five percent by dry weight. In a further embodiment,
the adhesive includes an amount of halogen-free flame retardant of
about fifty percent by dry weight. In various embodiments, the
adhesive is formed into a layer that may be laminated in production
of the EMI shield.
[0032] The adhesive may include any of a wide range of flame
retardants, including environmentally friendly flame retardants
that are substantially free or entirely free of halogens (e.g.,
bromines, chlorines, etc.). Particular examples of commercially
available halogen-free phosphorous-based flame retardants are sold
by Bostik, Inc. of Middleton, Mass. and Apex Chemical Company of
Spartanburg, S.C. Other exemplary flame retardants that can be used
include mineral oxides (e.g., magnesium hydroxide, antimony oxide,
etc.), metal hydrates (e.g., aluminum trihydrate, etc.) boron
compounds (e.g., boric acid, borax, etc.), melamines, and
silicones.
[0033] The following non-limiting examples, flammability test
results, tables (FIGS. 4 and 5), and line graphs (FIGS. 2, 3, and
6-12) help to illustrate various aspects of the EMI shields
produced in accordance with principles of the invention. These
examples are provided for purposes of illustration only and not for
limitation.
[0034] For one particular series of tests, the test specimens
included a commercially available Woodbridge four pound per cubic
foot density urethane foam 0.125 inches thick by 0.5 inches wide.
This foam was made in a layer thickness of 3.0 millimeters, which
is suitable for a UL sample. The test specimens further included an
electrically conductive metallized fabric material laminated to an
adhesive layer. The adhesive layer included a polyester adhesive
with about fifty-five percent by dry weight of a halogen-free
phosphorous-based flame retardant. Specifically, the adhesive layer
included 10-336 adhesive produced by Bostik, Inc. having a
thickness of about 0.0025 inches. Aspects of the invention,
however, are not limited to this particular type and kind of
adhesive.
[0035] In this series of tests, the fabric was provided with
urethane that did not include flame retardant (Non-FR urethane).
The Non-FR urethane coating included about eighteen percent
urethane solids such that the weight pick-up from the Non-FR
urethane coating was about 0.15 ounces per square yard (opsy).
Further, the fabric was laminated using a flat bed laminator set at
two hundred sixty degrees Fahrenheit at approximately fifteen feet
per minute (although other suitable means can also be employed).
The fabric and adhesive layer may also be trimmed to any suitable
size or shape.
[0036] The foam was joined together with the fabric and adhesive
layer using a series of heated dies to form the shield in the
desired shape. Samples of this shield embodiment having dimensions
of approximately 3.0 millimeters thick by 12.5 millimeters wide by
125 millimeters long were then tested per the UL94 flame rating of
V0. The exemplary flammability test results are set forth below in
Table 1 for purposes of illustration only. TABLE-US-00001 TABLE 1
Sample T1 T2 T3 Result 1 6 0 0 V0 2 5 0 0 V0 3 7 0 0 V0 4 8 0 0 V0
5 5 1 0 V0 Total Afterflame 32
[0037] As shown in Table 1 above, this particular embodiment of the
EMI shield included at least an effective amount of halogen-free
flame retardant within the adhesive to provide the shield with a
UL94 flame rating of V0.
[0038] FIG. 12 illustrates the bonding strength of this particular
adhesive (having about fifty-five percent by dry weight of a
halogen-free phosphorous-based flame retardant) between the
metallized fabric and a one-millimeter thick polyester film scrim.
The averaging bonding strength of this particular adhesive between
the metallized fabric and scrim was about thirty-five ounces per
inch width. The desired bonding strength, however, can vary
depending, for example, on the particular application in which the
EMI shield will be used.
[0039] For another series of tests, the test specimens included a
commercially available Woodbridge four pound per cubic foot density
urethane foam 0.125 inches thick by 0.5 inches wide. This foam was
made in a layer thickness of 3.0 millimeters, which is suitable for
a UL sample. The test specimens further included an electrically
conductive metallized fabric material laminated to an adhesive
layer. The adhesive layer included a polyester adhesive (e.g.,
10-335 adhesive produced by Bostik, Inc., etc.) with about
sixty-three percent by dry weight of a halogen-free
phosphorous-based flame retardant.
[0040] In this series of tests, the fabric was not provided with a
flame retardant. Further, the fabric was laminated using a flat bed
laminator set at two hundred sixty degrees Fahrenheit at
approximately fifteen feet per minute (although other suitable
means can also be employed). The fabric and adhesive layer may also
be trimmed to any suitable size or shape.
[0041] The foam was joined together with the fabric and adhesive
layer using a series of heated dies to form the shield in the
desired shape. Samples of this shield embodiment having dimensions
of approximately 3.0 millimeters thick by 12.5 millimeters wide by
125 millimeters long were then tested per the UL94 flame rating of
V0. The exemplary flammability test results are set forth below in
Table 2 for purposes of illustration only. TABLE-US-00002 TABLE 2
Sample T1 T2 T3 Result 1 9 0 0 V0 2 4 2 3 V0 3 14 0 3 V1 4 6 1 3 V0
5 9 1 3 V0 Total Afterflame 46
[0042] As shown in Table 2, this particular embodiment of the EMI
shield included at least an effective amount of halogen-free flame
retardant within the adhesive to provide the shield with a UL94
flame rating of V1. These flammability results may be suitable for
some applications as the desired flame rating can vary depending,
for example, on the particular application in which the EMI shield
will be used.
[0043] FIG. 2 illustrates the bonding strength of this particular
adhesive (having about sixty-three percent by dry weight of a
halogen-free phosphorous-based flame retardant) to the foam
(represented by line 200) and to a polyester film scrim
(represented by line 210) attached to the foam. As shown in FIG. 2,
the average bonding strength between this particular adhesive and
foam was about 4.6 ounces per inch width, and the average bonding
strength between this particular adhesive and scrim was about 4.2
ounces per inch width. The desired bonding strength, however, can
vary depending, for example, on the particular application in which
the EMI shield will be used.
[0044] For another series of tests, the test specimens included a
commercially available Woodbridge four pound per cubic foot density
urethane foam 0.125 inches thick by 0.5 inches wide. This foam was
made in a layer thickness of 3.0 millimeters, which is suitable for
a UL sample. The test specimens further included an electrically
conductive metallized fabric material that was again laminated to
an adhesive layer. The adhesive layer included about sixty-three
percent by dry weight of a halogen-free phosphorous-based flame
retardant.
[0045] But unlike the above test specimens, the fabric was provided
with a material (e.g., coating) that included halogen-free flame
retardant and urethane such that the weight pick-up therefrom (from
the material including the halogen-free flame retardant and
urethane) was about 0.27 ounces per square yard (opsy). The
halogen-free flame retardant was a water-based urethane dispersion
(having about thirteen percent solids by weight) including about
fifteen percent by weight of cyclic phosphonate esters with the
remaining balance being de-ionized water. This phosphorous-based
flame retardant liquid was then applied to the fabric by dipping
the fabric into the flame retardant. The excess flame retardant was
removed from the fabric (e.g., by squeezing the fabric with a pair
of rubber nip rollers at about twenty pounds per square inch, etc.)
and then drying the fabric in an oven when the oven temperature is
at about three hundred twenty degrees Fahrenheit for twenty five
minutes residence time in the oven. After drying, the flame
retardant urethane coating included about fifty-four percent
phosphorous-based flame retardant and about forty-six percent
urethane.
[0046] In this particular embodiment, the fabric was laminated
using a flat bed laminator set at about two hundred sixty degrees
Fahrenheit at approximately fifteen feet per minute (although it
may be laminated using other suitable means for achieving a desired
adherence). The foam was joined together with the electrically
conductive layer and the adhesive laminate using a series of heated
dies to form the shield in the desired shape. Samples of this
embodiment of a shield having dimensions of approximately 3.0
millimeters thick by 12.5 millimeters wide by 125 millimeters long
were then tested per the UL94 flame rating of V0. The shield of
this embodiment in which the fabric was provided with halogen-free
flame retardant, in combination with an adhesive loaded with about
sixty-three percent by dry weight of halogen-free flame retardant,
met the UL94 flame rating as V0 as shown in Table 3 below.
TABLE-US-00003 TABLE 3 Sample T1 T2 T3 Result 1 6 0 1 V0 2 5 0 1 V0
3 6 1 1 V0 4 5 0 0 V0 5 5 0 1 V0 Total Afterflame 28
[0047] For another series of tests, the test specimens included a
commercially available Woodbridge four pound per cubic foot density
urethane foam 0.125 inches thick by 0.5 inches wide. This foam was
made in a layer thickness of 3.0 millimeters, which is suitable for
a UL sample. The test specimens further included an electrically
conductive metallized fabric material that was laminated to an
adhesive layer. The adhesive layer included a polyester adhesive
(e.g., 10-335 adhesive produced by Bostik, Inc., etc.) with about
fifty percent by dry weight of a halogen-free phosphorous-based
flame retardant.
[0048] The fabric was provided with a material (e.g., coating) that
included halogen-free flame retardant and urethane such that the
weight pick-up therefrom was about 0.27 ounces per square yard
(opsy). In this particular embodiment, the halogen-free flame
retardant was a water-based urethane dispersion (having about
thirteen percent solids by weight) including about fifteen percent
by weight of cyclic phosphonate esters with the remaining balance
being de-ionized water. This phosphorous-based flame retardant
liquid was applied to the metallized fabric layer by dipping the
metallized fabric into the flame retardant. The excess flame
retardant was removed from the metallized fabric (e.g., by
squeezing the fabric with a pair of rubber nip rollers at twenty
pounds per square inch, etc.) and then drying the metallized fabric
in an oven when the oven temperature is at about three hundred
twenty degrees Fahrenheit for twenty five minutes residence time in
the oven. After drying, the flame retardant urethane coating
included about fifty-four percent phosphorous-based flame retardant
and about forty-six percent urethane.
[0049] In this particular embodiment, the fabric was laminated
using a flat bed laminator set at about two hundred sixty degrees
Fahrenheit at approximately fifteen feet per minute (although it
may be laminated using other suitable means for achieving a desired
adherence). The foam was joined together with the electrically
conductive layer and the adhesive laminate using a series of heated
dies to form the shield in the desired shape. Samples of this
embodiment of a shield having dimensions of approximately 3.0
millimeters thick by 12.5 millimeters wide by 125 millimeters long
were tested per the UL94 flame rating of V0. As shown in Table 4
below, the shield of this embodiment in which the fabric was
provided with halogen-free flame retardant, in combination with an
adhesive loaded with about fifty percent by dry weight of
halogen-free flame retardant, met the UL94 flame ratings of V0.
TABLE-US-00004 TABLE 4 Sample T1 T2 T3 Result 1 5 2 1 V0 2 5 0 1 V0
3 4 0 1 V0 4 5 1 1 V0 5 5 0 1 V0 Total Afterflame 27
[0050] FIG. 3 illustrates the bonding strength of this particular
adhesive (having about fifty percent by dry weight of halogen-free
phosphorous-based flame retardant) to the foam (represented by line
300) and to a polyester film scrim (represented by line 310)
attached to the foam. As shown in FIG. 3, the bonding strength
between this particular adhesive and foam was sufficiently strong
to tear the foam, and the average bonding strength between this
particular adhesive and scrim was about 55.3 ounces per inch width.
The desired bonding strength, however, can vary depending, for
example, on the particular application in which the EMI shield will
be used.
[0051] In the latter two tests described above, the fabric was
provided with halogen-free flame retardant urethane such that the
weight pick-up therefrom was about 0.27 ounces per square yard
(opsy). In other embodiments, however, the electrically conductive
fabric (e.g., nylon ripstop (NRS) fabrics, mesh fabrics, taffeta
fabrics, woven fabrics, non-woven fabrics, knitted fabrics, etc.)
can be provided with (e.g., coated, impregnated, combinations
thereof, etc.) a different amount of halogen-free flame retardant.
Various embodiments include an electrically conductive fabric
provided with halogen-free flame retardant urethane (e.g., coating,
etc.) such that the weight pick-up therefrom is between about 0.16
opsy and about 0.33 opsy (e.g., about 0.16 opsy, about 0.20 opsy,
about 0.26 opsy, about 0.27 opsy, about 0.33 opsy, etc.).
[0052] In various embodiments, an electrically conductive fabric
includes a halogen-free flame retardant urethane coating having a
thickness of about one micron or less. In such embodiments, the
thickness of the halogen-free flame retardant urethane coating can
vary across the surface of the fabric. Alternatively, the thickness
of the halogen-free flame retardant urethane coating can be
substantially uniform across the surface of the fabric. To help
maintain electrical conductivity, the fabric in various embodiments
is not entirely permeated or encapsulated with flame retardant
urethane.
[0053] In some embodiments, the electrically conductive fabric may
be provided with a halogen-free corrosion inhibitor (e.g.,
benzotriazole, or other suitable corrosion inhibitor, for example,
selected from the azole family and/or pyrole family, etc.).
Depending on the particular corrosion inhibitor used, the corrosion
inhibitor may function as a halogen-free flame retardant. In such
embodiments, the corrosion inhibitor may thus be referred to herein
as a halogen-free flame retardant. In yet other embodiments, the
electrically conductive fabric is provided (e.g., coated, etc.)
with both a corrosion inhibitor and flame retardant.
[0054] In still other embodiments, the electrically conductive
fabric is provided (e.g., coated, etc.) with a material that does
not including any halogen-free flame retardant. For example, in the
test first described above, the electrically conductive layer was
provided with a Non-FR urethane coating having about eighteen
percent urethane solids such that the weight pick-up from the
Non-FR urethane coating was about 0.15 opsy. Yet other embodiments
include an electrically conductive fabric provided with Non-FR
urethane (e.g., coating, etc.) having about ten percent to about
eighteen percent urethane solids such that the weight pick-up on
the fabric is between about 0.05 opsy and about 0.35 opsy (e.g.,
about 0.05 opsy, about 0.15 opsy, about 0.35 opsy, etc.).
[0055] By way of example, FIG. 4 lists three exemplary materials
(NRS, mesh, and taffeta) that are used in various embodiments of
the invention. Any one of the fabrics listed in FIG. 4 can be
bonded to a resilient core member (e.g., urethane foam, etc.) with
an adhesive that includes halogen-free flame retardant, thereby
forming an EMI shield according to various embodiments of the
invention. FIG. 4 also provides surface resistivity of these
exemplary fabrics when uncoated and when coated with halogen-free
flame retardant urethane. As shown in FIG. 4, the coated and
uncoated fabrics all have a surface resistivity of less than 0.10
ohms/sq. In addition, FIG. 4 also indicates that some of the coated
fabrics achieve a UL rating of HB, such as the coated NRS.
[0056] While the halogen-free flame retardant provided to the
fabrics in FIG. 4 was not enough to significantly increase surface
resistivity, it was a sufficient amount so as to allow the adhesive
to be loaded with less halogen-free flame retardant in order to
obtain a higher adhesive bond strength and also achieve a UL94
flame rating of V0 for the overall EMI shield product.
Alternatively, other flame retardants, other amounts of flame
retardants, and other materials besides the fabrics shown in FIG. 4
can be used for an EMI shield of the present invention.
[0057] In some embodiments, the halogen-free flame retardant
urethane provided (e.g., applied, coated, impregnated, combinations
thereof, etc.) to the electrically conductive portion is formed,
for example, by combining together while substantially
continuously, vigorously mixing in the following exemplary ratio
and order about thirty-five percent by weight of Soluol 1024
water-based urethane dispersion (having about thirty-seven percent
solids) including about fifty percent by weight of de-ionized water
and about fifteen percent by weight of phosphorous-based flame
retardant. The resulting flame retardant urethane includes about
twenty-nine percent solids and has a viscosity of about twenty
centipoise per second (cps). Accordingly, and after drying in this
particular embodiment, the halogen-free flame retardant urethane
provided to the electrically conductive portion includes about
forty-six percent by dry weight of urethane and about fifty-four
percent by dry weight of flame retardant. In another embodiment,
however, the electrically conductive portion is provided (e.g.,
applied, coated, impregnated, combinations thereof, etc.) with a
halogen-free flame retardant urethane that includes about fifty-two
percent by dry weight of halogen-free flame retardant and about of
about forty-eight by dry weight of urethane. Exemplary
phosphorous-based flame retardants that can be used include cyclic
phosphonate ester blends available from Sovereign Specialty
Chemicals, Inc. of Chicago, Ill. and/or from AKSO Nobel Phosphorous
Chemicals, Inc. of Dobbs Ferry, N.Y. Alternatively, other suitable
flame retardants can be used including mineral oxides (e.g.,
magnesium hydroxide, antimony oxide, etc.), metal hydrates (e.g.,
aluminum trihydrate, etc.) boron compounds (e.g., boric acid,
borax, etc.), melamines, silicones, among others.
[0058] In various embodiments, the resilient core member (e.g.,
urethane foam, etc.) is also provided with flame retardant. For
example, various embodiments include a resilient core member
provided (e.g., impregnated with, etc.) with an antimony flame
retardant such that the resilient core member is able to achieve a
UL rating of HF1.
[0059] Accordingly, various EMI shields of the present invention
include a core member, an electrically conductive portion, and an
adhesive bonding the electrically conductive portion to the core
member, wherein the core member, the electrically conductive
portion, and the adhesive are each provided with (e.g., coated,
impregnated, combination thereof, etc.) a flame retardant. In these
embodiments, the flame retardant applied to the electrically
conductive portion can be a corrosion inhibitor, such as
benzotriazole or other suitable corrosion inhibitor, for example,
selected from the azole family and/or pyrole family, etc.
[0060] FIG. 5 is a table of data collected during crush and fold
testing of a nylon ripstop (NRS) fabric coated with urethane that
did not include flame retardant (Non-FR urethane), and a NRS fabric
coated with halogen-free flame retardant urethane (FR urethane).
For this particular example, the first NRS fabric was provided with
an amount of Non-FR urethane such that the weight pick-up therefrom
was about 0.23 opsy, and the other NRS fabric was provided with an
amount of FR urethane such that the weight pick-up therefrom was
about 0.27 opsy. Generally, crush and fold tests measure abuse
resistance of a plated metal fabric by folding and crumpling the
fabric. In this particular example, the NRS fabric coated with
Non-FR urethane and the NRS fabric coated with halogen-free flame
retardant urethane were both tested for shielding effectiveness
between five and one thousand megahertz and for surface
resistivity. The fabrics were then folded in quarters, rolled into
a cylinder, and crushed in a ten milliliter syringe using a five
pound weight. The testing was repeated until the average shielding
effectiveness dropped below sixty decibels across the frequency
range.
[0061] FIG. 6 is an exemplary line graph created from the surface
resistivity data shown in FIG. 5. In FIG. 6, line 600 represents
surface resistivity for the NRS fabric coated with Non-FR urethane,
and line 610 represents surface resistivity for the NRS fabric
coated with halogen-free flame retardant urethane.
[0062] FIG. 7 is an exemplary line graph showing surface
resistivity versus number of cycles during inflated diaphragm
abrasion testing of NRS fabric coated with an amount of Non-FR
urethane such that the weight pick-up therefrom was about 0.23
opsy, and a NRS fabric coated with an amount of halogen-free flame
retardant urethane such that the weight pick-up therefrom was about
0.27 opsy. In FIG. 7, line 700 represents surface resistivity for
the NRS fabric coated with Non-FR urethane, and line 710 represents
surface resistivity for the NRS fabric coated with halogen-free
flame retardant urethane.
[0063] FIG. 8 is an exemplary line graph of shielding effectiveness
(in decibels) versus electromagnetic interference frequency (in
megahertz) for a nickel copper NRS fabric coated with an amount of
Non-FR urethane such that the weight pick-up therefrom was about
0.23 opsy, and a nickel copper NRS fabric coated with halogen-free
flame retardant urethane such that the weight pick-up therefrom was
0.27 opsy. In FIG. 8, line 800 represents shielding effectiveness
for the NRS fabric coated with Non-FR urethane, and line 810
represents shielding effectiveness for the NRS fabric coated with
halogen-free flame retardant urethane. As noted in FIG. 8, the NRS
fabric coated with Non-FR urethane had an average shielding
effectiveness of about eighty two decibels across the frequency
range of five to one thousand megahertz. The NRS fabric coated with
halogen-free flame retardant urethane had an average shielding
effectiveness of about seventy five decibels across the frequency
range of five to one thousand megahertz.
[0064] FIG. 9 is an exemplary line graph of shielding effectiveness
(in decibels) versus electromagnetic interference frequency (in
megahertz) for the nickel copper NRS fabrics shown in FIG. 8 but
after one week of environmental exposure within a humidity and
temperature chamber at sixty degrees Celsius and ninety percent
relative humidity. In FIG. 9, line 900 represents shielding
effectiveness for the NRS fabric coated with Non-FR urethane, and
line 910 represents shielding effectiveness for the NRS fabric
coated with halogen-free flame retardant urethane. As noted in FIG.
9, the NRS fabric coated with Non-FR urethane had an average
shielding effectiveness of about eighty one decibels across the
frequency range of five to one thousand megahertz. The NRS fabric
coated with halogen-free flame retardant urethane had an average
shielding effectiveness of about seventy eight decibels across the
frequency range of five to one thousand megahertz.
[0065] FIG. 10 is another exemplary line graph of shielding
effectiveness (in decibels) versus electromagnetic interference
frequency (in megahertz) for the nickel copper NRS fabrics shown in
FIGS. 8 and 9 but after two weeks of environmental exposure within
a humidity and temperature chamber at sixty degrees Celsius and
ninety percent relative humidity. In FIG. 10, line 1000 represents
shielding effectiveness for the NRS fabric coated with Non-FR
urethane, and line 1010 represents shielding effectiveness for the
NRS fabric coated with halogen-free flame retardant urethane. As
noted in FIG. 10, the NRS fabric coated with Non-FR urethane had an
average shielding effectiveness of about eighty one decibels across
the frequency range of five to one thousand megahertz. The NRS
fabric coated with halogen-free flame retardant urethane had an
average shielding effectiveness of about seventy eight decibels
across the frequency range of five to one thousand megahertz.
[0066] FIG. 11 is another exemplary line graph of shielding
effectiveness versus electromagnetic interference frequency for the
nickel copper NRS fabric coated with the FR urethane shown in FIGS.
8-10 but after eight weeks of environmental exposure within a
humidity and temperature chamber at sixty degrees Celsius and
ninety percent relative humidity. In FIG. 11, the line 1110
represents shielding effectiveness for the NRS fabric coated with
halogen-free flame retardant urethane. As noted in FIG. 11, the NRS
fabric coated with halogen-free flame retardant urethane had an
average shielding effectiveness of about seventy seven decibels
across the frequency range of five to one thousand megahertz.
[0067] In various embodiments, an EMI shield generally includes a
resilient core member and an electrically conductive layer. In
these particular embodiments, the electrically conductive layer is
bonded to the core member with an adhesive layer having a thickness
of about 0.0025. The adhesive layer is formed from 10-336 adhesive
sold by Bostik, Inc. The inventor hereof has recognized that with
this particular adhesive, the EMI shield can achieve a UL94 flame
rating of V0 without any flame retardant being provided to the
electrically conductive layer. For example, the electrically
conductive layer in one embodiment includes a Non-FR urethane
coating having about eighteen percent urethane solids such that the
weight pick-up from the Non-FR urethane coating was about 0.15
opsy. Yet other embodiments include an electrically conductive
layer provided with Non-FR urethane (e.g., coating, etc.) having
about ten percent to about eighteen percent urethane solids such
that the weight pick-up on the fabric is between about 0.05 opsy
and about 0.35 opsy (e.g., about 0.05 opsy, about 0.15 opsy, about
0.35 opsy, etc.).
[0068] In further embodiments, an EMI shield generally includes a
resilient core member and an electrically conductive layer. An
adhesive, which include halogen-free flame retardant, bonds the
electrically conductive layer to the core member. In these
particular embodiments, the electrically conductive layer is
provided with (e.g., coated, impregnated, combinations thereof,
etc.) a halogen-free corrosion inhibitor (e.g., benzotriazole, or
other suitable corrosion inhibitor, for example, selected from the
azole family and/or pyrole family, etc.). Depending on the
particular corrosion inhibitor used, the corrosion inhibitor may
function as a halogen-free flame retardant, in which case, the
corrosion inhibitor may thus be referred to herein as a
halogen-free flame retardant. This corrosion inhibitor can be added
to a urethane coating, which is applied to the electrically
conductive layer. The inventor hereof has recognized that when
halogen-free EMI shields are exposed to high temperature and
humidity (e.g., sixty degrees Celsius or higher temperatures,
ninety percent relative humidity or higher) for several days, a
small amount of corrosion may form when the EMI shields are in
contact with certain metals. Adding a corrosion inhibitor to the
EMI shield can greatly improve the corrosion resistance of the
halogen-free EMI shield in a high temperature and high humidity
environment. In various embodiments, the electrically conductive
layer of the EMI shield is provided with (e.g., coated,
impregnated, combinations thereof, etc.) urethane that includes a
corrosion inhibitor additive to thereby help protect the EMI shield
from corrosion in high temperature and humidity applications. In
one embodiment of a halogen-free EMI shield, the electrically
conductive layer is provided or coated with liquid urethane having
an amount of Benzotriazole corrosion inhibitor of at least about
two percent by liquid weight. In another embodiment of a
halogen-free EMI shield, the electrically conductive layer is
provided or coated with liquid urethane having an amount of
Benzotriazole corrosion inhibitor of at least about one percent by
liquid weight. In a further embodiment of a halogen-free EMI
shield, the electrically conductive layer is provided or coated
with a dry urethane film having an amount of Benzotriazole
corrosion inhibitor of at least about four percent by dry weight.
Alternatively, other suitable corrosion inhibitors and/or in other
amounts can be used depending on the particular application in
which the EMI shield will be used.
[0069] Accordingly, various embodiments of the present invention
include fabric-over-foam EMI shields that are formed from
environmentally friendly retardants (e.g., halogen-free flame
retardants, etc.) and still are able achieve a UL flame rating of
V0 while also having a bond strength of at least ten ounces per
inch width (e.g., as determined by standard testing, for example,
such as a one hundred eighty degree peel at twelve inches per
minute, etc.) to a foam and a scrim attached to the foam and
retaining properties suitable (e.g., shielding effectiveness, bulk
resistivity, etc.) for EMI shielding applications.
[0070] The teachings of the present invention can be applied in a
wide range of applications. Accordingly, the specific references to
electromagnetic interference shielding applications should not be
construed as limiting the scope of the present invention to use in
only electromagnetic interference shielding applications.
[0071] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention.
* * * * *